Electrophoretic mobilities of allophane and imogolite were determined by microelectrophoresis. The influence of pre-treatments, viz., air-drying and pre-acidification, on the isoelectric point (i.e.p.) of allophane was investigated. The i.e.p.(pH ca. 5.8) of Na-saturated allophane was shifted to higher pH (7.3) by pre-acidification, while the effect of airdrying on the i, e.p, was not so significant. Imogolite particles began to flocculate as pH increased beyond 7 to 7.5. The pH at which imogolite had no charge (zero electrophoretic mobility) was shown to be 9 to 10. The floccule of imogolite dissolved in part as time passed at pH 12. The different electrokinetic behavior between allophane and imogolite at higher pH was discussed in relation to the structural differences between the two.

View full abstract

Electrophoretic mobilities of allophane-imogolite mixtures in different proportions were determined at a fixed pH of 10.8-10.9. The absolute value of electrophoretic mobility of allophane significantly decreased by the addition of a small amount of imogolite. In a 30 % imogolite and 70% allophane mixture, allophane was flocculated perfectly with imogolite, and showed zero electrophoretic mobility. Flocculation of allophane with imogolite was also observed when alkali-dispersed allophane was mixed with imogolite which had been flocculated at pH 10.8. The flocculation of allophane with imogolite under a strong alkaline condition may be due to immobilization of allophane by newly-formed network of imogolite particles.

View full abstract

The flocculation rate of selected clays, i.e., montmorillonite, hydrated halloysite, allophane and imogolite by several electrolytes was investigated spectrophotometrically. In general, flocculation power of inorganic electrolytes showed considerable dependence upon the valence of the counter ions. Organic electrolytes exhibited significantly higher flocculating power than inorganic electrolytes. In the case of imogolite, flocculation rate considerably varied because of the introduced fine air bubbles. The valence effect of anion on the flocculation of imogolite was not so significant. The effect of particle size on this method was also discussed.

View full abstract

Flotation and electrophoretic mobility of selected clays, i.e., allophane, imogolite, and layer-type clay minerals, were investigated as a function of pH and concentration of several ionic surface active agents. Cationic surface active agents were effectively adsorbed by clay surfaces where negative charges predominated, while an anionic surface active agent was adsorbed by allophane and imogolite in acid solutions where positive charges predominated. The maximum flotation of clay particles with surface active agents was observed when the electrophoretic mobility of the clays approached to zero. Imogolite particles were also removed by flotation with an anionic surface active agent at concentrations above 1.67×10^-4 M at pH 9.1-9.3 where allophane particles were not removed. In the case of 1: 1 type clay minerals, only small amounts of particles were removed with cationic surface active agents.

View full abstract

A structure model of allophane was proposed from results obtained by X-ray radial distribution, X-ray fluorescence and nuclear magnetic resonance analyses. Al atoms in allophane were in four-fold coordination as well as in six-fold coordination. The linkages of Sitetrahedra, Al-tetrahedra and Al-octahedra in allophane were considered to be two-dimensional by radial distribution analysis. This two-dimensional arrangement was further confirmed by the fact that the differential radial distribution curve of allophane fitted very closely to the theoretical differential radial distribution curve of kaolin. The authors gave a structual scheme for allophane, which consists of a kaolin-like sheet structure with Si atoms in the tetrahedral layer being partially substituted by Al atoms. This kaolin-like structure has cation vacant sites in the tetrahedral layer in Al₂O₃-rich allophane and it has those in the octahedral layer in SiO₂-rich allophane. The OH contents calculated from the structure models are in good agreement with those estimated by nuclear magnetic resonance analysis.

View full abstract

X-ray, chemical, DTA (micro and macro), TG, and infrared data for five Mg-chlorites and four interstratified Mg-chlorite/ saponites collected from the intensively argillized zone of Kuroko and Kuroko-type gypsum deposits in Japan are presented. The Mg-chlorites with variable aluminum contents belong to trioctahedral series but are deficient in octahedral cations by a substitution of 2A1 for 3Mg. The interstratified Mgchlorite/ saponites, being relatively rich in silicon compared with the Mg-chlorites, are composed of an irregularly interstratified mineral having small amounts of saponite layers and a 1: 1 regularly interstratified mineral. Discussions are made on the characteristics of these minerals in relation to well-crystallized Mg-chlorite, on previous data of magnesian chlorite clay minerals from Kuroko deposits, and also on possible interlayer structures of the interstratified minerals.

View full abstract